This invention relates to refractory-oxide-based cermets and method and, more particularly, to refractory-oxide-based elongated incandescent radiators which are particularly adapted for use as light sources which can be self-resistance heated to a state of incandescence, and to methods for making same.
Refractory-oxide-based incandescent members which are particularly adapted for use as lamp filaments are known, such as described in U.S. Pat. No. 3,412,286, dated Nov. 19, 1968. The refractory oxide radiators are potentially superior to tungsten with respect to spectral emission characteristics. Practical application of such members in lamps has been impeded by several properties of oxide ceramics such as very low electrical conductivity at room temperatures, a positive temperature coefficient of conductivity, and poor thermal shock resistance. Attempts to overcome these difficulties have included the use of preheaters to raise the ceramic into its self-conducting temperature range, ballasts to stabilize the filament current and prevent current "run-away", and carefully controlled heat-up and cool-down rates to minimize thermally shocking the elements to prevent their fracture.